The present invention relates to curable phosphorus element-containing epoxy resin formulations, and particularly to formulations useful for making laminates for printed wiring boards and composite materials.
It is known to make electrical laminates and other composites from a fibrous reinforcement and an epoxy-containing matrix resin. Examples of suitable processes usually contain the following steps:
(1) an epoxy-containing formulation is applied to or impregnated into a substrate by rolling, dipping, spraying, other known techniques and/or combinations thereof. The substrate is typically a woven or nonwoven fiber mat containing, for instance, glass fibers or paper.
(2) The impregnated substrate is xe2x80x9cB-stagedxe2x80x9d by heating at a temperature sufficient to draw off solvent in the epoxy formulation and optionally to partially cure the epoxy formulation, so that the impregnated substrate can be handled easily. The xe2x80x9cB-stagingxe2x80x9d step is usually carried out at a temperature of from 90xc2x0 C. to 210xc2x0 C. and for a time of from 1 minute to 15 minutes. The impregnated substrate that results from B-staging is called a xe2x80x9cprepreg.xe2x80x9d The temperature is most commonly 100xc2x0 C. for composites and 130xc2x0 C. to 200xc2x0 C. for electrical laminates.
(3) One or more sheets of prepreg are stacked or laid up in alternating layers with one or more sheets of a conductive material, such as copper foil, if an electrical laminate is desired.
(4) The laid-up sheets are pressed at high temperature and pressure for a time sufficient to cure the resin and form a laminate. The temperature of this lamination step is usually between 100xc2x0 C. and 230xc2x0 C., and is most often between 165xc2x0 C. and 190xc2x0 C. The lamination step may also be carried out in two or more stages, such as a first stage between 100xc2x0 C. and 150xc2x0 C. and a second stage at between 165xc2x0 C. and 190xc2x0 C. The pressure is usually between 50 N/cm2 and 500 N/cm2. The lamination step is usually carried out for a time of from 1 minute to 200 minutes, and most often for 45 minutes to 90 minutes. The lamination step may optionally be carried out at higher temperatures for shorter times (such as in continuous lamination processes) or for longer times at lower temperatures (such as in low energy press processes).
(5) Optionally, the resulting laminate, for example, a copper-clad laminate, may be post-treated by heating for a time at high temperature and ambient pressure. The temperature of post-treatment is usually between 120xc2x0 C. and 250xc2x0 C. The post-treatment time usually is between 30 minutes and 12 hours.
It is conventional in the preparation of epoxy-containing laminates to incorporate into the epoxy resin composition various additives to improve the flame-retardancy of the resulting laminate. Many types of flame retardant additives have been suggested, but the additives which are most widely used commercially are halogen-containing additives, such as tetrabromodiphenylolpropane, or epoxy resins prepared by reacting diglycidyl ether of bisphenol-A with tetrabromodiphenylolpropane. Typically, in order to reach the desired fire retardancy level (V-0 in the standard xe2x80x9cUnderwriters Laboratoryxe2x80x9d test method UL 94), levels of such bromine-containing flame retardant additives are required which provide a bromine content of from 10 wt % to 25 wt % based on the total polymer weight in the product.
Although halogen-containing fire-retardant additives such as tetrabromodiphenylolpropane, are effective, they are considered by some to be undesirable from an environmental standpoint, and in recent years there has been increasing interest in the formulation of halogen-free epoxy resins, which are able to meet the fire retardancy requirements.
Proposals have been made to use phosphorus-based flame retardants instead of halogenated fire retardants in epoxy resin formulations as described in, for example, EP A 0384939, EP A 0384940, EP A 0408990, DE A 4308184, DE A 4308185, DE A 4308187, WO A 96/07685, and WO A 96/07686. In these formulations a phosphorus flame retardant is pre-reacted with an epoxy resin to form a di- or multifunctional epoxy resin which is then cured with an amino cross-linker such as dicyandiamide, sulfanilamide, or some other nitrogen element-containing cross-linker to form a network.
There are some commercially available phosphorus-based fire retardant additives which may be useful for replacing halogen-containing fire-retardant additives. For example, Amgard(trademark) V19 and Antiblaze(trademark) 1045 (previously Amgard(trademark) P45) supplied by Albright and Wilson Ltd, United Kingdom, are commercially available phosphonic acid ester fire retardant materials. These phosphonic acid esters, may be solids or liquids.
Alkyl and aryl substituted phosphonic acid esters are compatible with epoxy resins. In particular, lower alkyl (i.e., C1-C4) esters of phosphonic acid are of value because they contain a high proportion of phosphorus, and are thus able to impart good fire retardant properties upon resins in which they are incorporated. However, the phosphonic acid esters are not satisfactory as a substitute for halogenated flame retardants in epoxy resins for the production of electrical laminates, because the use of phosphonic acid esters, used in amounts sufficient to provide the necessary flame retardancy, increases the tendency of the resulting cured epoxy resin to absorb moisture. The moisture absorbency of a cured laminate board is very significant, because laminates containing high levels of moisture tend to blister and fail, when introduced to a bath of liquid solder at temperatures around 260xc2x0 C., a typical step in the manufacture of printed wiring boards.
Another system, which utilizes a phosphorus-based flame retardant, is described in EP A 0754728. EP A 0754728 describes the production of flame retardant epoxy resin systems by blending epoxy resins with a cyclic phosphonate as a flame retardant and incorporating the cyclic phosphonate into the cured resin. The epoxide resin and phosphonate mixture is crosslinked with a polyamine such as triethylamine, tetra amine, polyamido amines, multi basic acids or their anhydrides for example phthalic anhydride or hexahydrophthalic anhydride. EP A 0754728 indicates that large quantities, such as in excess of 18 wt %, of the phosphorus additive are needed in order for the resin system to meet UL 94 V-0.
WO 99/00451 also discloses flame retardant epoxy resin compositions utilizing phosphonic acid esters. WO 99/00451 discloses the reaction of a phosphonic acid ester with an epoxy resin in the presence of a catalyst and a nitrogen-containing crosslinking agent. The crosslinking agent has an amine functionality of at least 2 and is preferably dicyandiamide. The epoxy resins described in WO 99/00451 have improved flame retardant properties at low levels of phosphonic acid ester flame retardant. However, there is still a need in the industry for a flame retardant epoxy resin composition with improved Tg and flame retardancy.
The present invention is directed to epoxy resins which meet the desirable standards of fire retardancy without the need for halogen-containing flame retardants. The epoxy resin compositions of the present invention employ relatively low levels of a phosphorus element-containing compound in the resin (for example, to provide from about 0.2 wt % to about 3.5 wt % phosphorus in a solid resin or a solid curing formulation), together with particular combinations of a multi-functional phenolic hardener, an accelerator and a catalyst, and, in preferred embodiments, particular types of epoxy resins. The multi-functional phenolic hardeners, accelerators and catalysts are generally known p se, but their use in conjunction with low levels of fire retardants to obtain compositions which have both good fire retardancy, and yet sufficiently low water absorption has not hitherto been described.
According to one aspect of present invention, there is provided a flame retardant curable phosphorus element-containing epoxy resin composition substantially free of halogen, comprising:
(I) a non-halogenated epoxy resin material selected from:
(A) a non-halogenated phosphorus element-containing epoxy resin;
(B) a mixture of:
(1) a non-halognated, non-phosphorus element-containing epoxy resin, and
(2) a phosphorus element-containing compound; or
(C) the reaction product of:
(3) a non-halogenated epoxy resin; and
(4) a phosphorus element-containing compound; or
(D) a combination of tow or more components (A) to (C);
(II)
(E) a multi-funcitional phenolic crosslinking agent having a hydroxy functionality of at least 2;
(F) a material which forms a multi-functional phenolic cross-linking agent having a hydroxy functionality of at least 2 upon heating; preferably in amount of from about 50% to about 150% of the stoichiometric amount needed to cure the epoxy resin; or
(G) a mixture of components (A) and (B); and
(III) optionally, a catalyst capable of promoting the reaction of the phenolic/hydroxy group of the multi-functional phenolic crosslinking agent with the epoxy group of the epoxy resin material.
Another aspect of present invention is directed to providing a flame retardant hardener composition substantially free of halogen, comprising:
(a) (i) a multi-functional phenolic crosslinking agent having a hydroxy functionally of at least 2 or (ii) a material which forms a multi-functional phenolic cross-linking agent having a hydroxy functionality of at least 2 upon heating or (iii) a mixture of components (i) and (ii); preferably in an amount of from about 50% to 150% of the stoichiometric amount needed to cure an epoxy resin;
(b) a phosphorus element-containing compound; the phosphorus element-containing compound preferably having an amine, a phosphine, a phosphate, a hydroxy, an anhydride, or an acid functionality, and preferably, in an amount such as to provide from about 0.2 wt % to about 3.5 wt % phosphorus in a final curing formulation composition; and
(c) optionally, a Lewis acid inhibitor.
A preferred embodiment of the present invention includes an epoxy resin having a reduced number of aliphatic chain groups in the cured epoxy resin composites network. The lower number of aliphatic chain groups is believed to reduce the methane gas emissions during burning.
It has also been found that the reaction product or epoxy adduct produced by reacting a non-halogenated epoxy resin and a phosphorus element-containing compound surprisingly provides advantageous benefits when used for preparing the flame retardant formulations of the present invention. Accordingly, another aspect of the present invention is directed to a phosphorus element-containing epoxy resin adduct comprising the reaction product of (1) a non-halogenated epoxy resin; and (2) a phosphorus element-containing compound which is preferably a chain extender which has a functionality of from about 1 to about 3, more preferably from about 1.8 to about 2.2. The chain extender may be for example a hydroxy functional or an amine functional compound such as for example 10-(2xe2x80x2,5xe2x80x2-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.
In its broadest scope, the present invention is a flame retardant epoxy resin composition substantially free of halogen including: (I) a non-halogenated epoxy resin material with some specific amount of phosphorus element therein; and (II) a multi-functional phenolic crosslinking agent having a hydroxy functionality of at least 2. A resin which is xe2x80x9csubstantially free of halogenxe2x80x9d means that the resin is completely free of halogen, i.e. 0% halogen, or that the resin contains some minor amount of halogen that does not affect the properties or performance of the resin, and is not detrimental to the resin. xe2x80x9cSubstantially free of halogenxe2x80x9d, therefore, herein includes for example, wherein the resin contains up to about 10 weight percent halogen, but preferably contains less than about 10 weight percent, more preferably less than about 5 weight percent, even more preferably less than about 1 weight percent and most preferably zero weight percent of a halogen in the resin composition.
In order to obtain satisfactory flame retardancy and still provide the benefit of resistance to water absorption, it is important that the amount of the phosphorus element in the resin composition is from about 0.2 wt % to about 3.5 wt %, preferably from about 1 wt % to about 3 wt %, more preferably from about 1.5 wt % to about 2.8 wt %, based on the total amount of the solid curing resin composition.
The multi-functional phenolic cross-linker (II) of the present invention, also referred to interchangeably herein as a hardener or curing agent, preferably contains at least two or more functionalities. The crosslinker (II) may be selected from (E) a phenolic crosslinking agent having a functionality of at least 2; (F) a material or compound which forms a phenolic crosslinking agent having a functionality of at least 2, upon heating or (G) a mixture of components (A) and (B). The phenolic hardeners (II) are compounds, either polymeric or monomeric, which have at least 2 phenolic xe2x80x94OH (hydroxyl groups) capable of reacting with epoxy groups at elevated temperatures. The phenolic hardeners include various types of compounds such as:
a. Phenolic resins obtained from phenols or alkyl phenols and formaldehyde, such as phenol novolacs or resoles, as described in Lee and Neville, section 11-14;
b. 3,4,5-trihydroxybenzoic acid (also known as gallic acid) or its derivatives, or pyrogallol (also known as 1,2,3-trihydroxybenzol), or 1,2,4-trihydroxybenzol (also known as hydroxyhydrochinon);
c. 1,8,9-trihydroxyanthracene(also known as dithranol or 1,8,9-anthracentriol), or 1,2,10-trihydroxyanthracene (also known as anthrarobine);
d. 2,4,5-trihydroxypyrimidine;
e. tris(hydroxyphenyl)methane;
f. dicylcopentadiene phenol novolac;
g. tetraphenolethane; and
h. copolymer of styrene and hydroxystyrene.
The chemical structure of some of the phenolic hardeners (II) described above are as follows: 
The multi-functional phenolic cross-linker (II) is preferably a novolac or a cresol novolac obtained by the condensation of phenols, cresols, xylenols or other alkyl phenols with a formaldehyde. Also, in the present invention, the resoles may be used as the multi-functional phenolic cross-linker.
Preferably, the multi-functional phenolic cross-linker (II) of the present invention has the following chemical structural formula: 
wherein xe2x80x9cRxe2x80x9d is hydrogen or a C1-C3 alkyl, e.g., methyl; and xe2x80x9cnxe2x80x9d is 0 or an integer from 1 to 10. xe2x80x9cnxe2x80x9d preferably has an average value of from 0 to 5. The preferred crosslinker (II) is when R is preferably a hydrogen in the above Formula I.
Commercially available products having the above general Formula I for the crosslinking agent (II) include for example, Perstorp 85.36.28 which is a phenolic resin obtained from phenol and formaldehyde having an average Mettler softening point of 103xc2x0 C., melt viscosity at 150xc2x0 C.=1.2 Pa.s and a functionality of 4 to 5. Another example includes Durite SD 1731 from Borden Chemical of USA.
Examples of compounds (F) which form a phenolic crosslinking agent (II) upon heating include phenolic species obtained from heating benzoxazine, for example as illustrated in the following chemical equation: 
wherein n is greater than 1; and wherein Rxe2x80x2 and Rxe2x80x3 may be, independently and separately, the same or different hydrogen, an allyl group from C1-C10 such as methyl, a C6-C20 aromatic group such as phenyl or a C4-C20 cycloaliphatic group such as cyclohexane.
Examples of compounds (F) also include benzoxazine of phenolphthalein, benzoxazine of bisphenol-A, benzoxazine of bisphenol-F, benzoxazine of phenol novolac and the like. Mixtures of components (A) and (B) described above may also be used.
The multi-functional phenolic cross-linker (II) is preferably used in the epoxy resin composition in an amount of from about 50% to about 150% of the stoichiometric amount needed to cure the epoxy resin and more preferably from about 75% to about 125% of the stoichiometric amount needed to cure the epoxy resin, even more preferably from about 85% to about 110% of the stoichiometric amount needed to cure the epoxy resin.
Optionally, other co-cross-linking agents (VII) may be used in combination with the multi-functional phenolic cross-linking agent. Suitable multifunctional co-cross-linkers useful in the present invention are described in numerous references such as Vol. 6 Encyclopedia of Poly. Sci. and Eng., xe2x80x9cEpoxy Resinsxe2x80x9d at 348-56 (J. Wiley and Sons 1986).
Some of the co-cross-linkers (VII) useful in the present invention include, for example, anhydrides such as a carboxylic acid anhydrides, styrene maleic anhydride copolymers, maleic anhydride adducts of methylcyclopentadiene and the like; amino compounds such as dicydiamide, sulfanilamide, 2,4-diamino-6-phenyl-1,3,5 triazine, and the like; carboxylic acids such as salicylic acid, phthalic acid and the like; cyanate esters such as dicyanate of dicyclopentadienyl bisphenol, dicyanate of bisphenol-A and the like; isocyanates such as MDI, TDI and the like; and bismaleic triazines and the like.
In one preferred embodiment, for example, a nitrogen-containing cross-linker (VII) can be used as a subsidiary or co-cross-linker in addition to the multi-functional phenolic cross-linker (II). The nitrogen-containing co-cross-linking agent has an amine functionality of at least 2. Examples of suitable nitrogen-containing cross-linkers useful in the present invention may be found in WO 99/00451, incorporated herein by reference; and include for example, polyamines, polyamides, sulfanilamide, diaminodiphenylsulfone and diaminodiphenyl methane and dicyandiamide, substituted dicyandiamide, 2,4-diamino-6-phenyl-1,3,5-triazine. When a nitrogen-containing cross-linker is used in the present formulation, the preferred nitrogen-containing cross-linkers are dicyandiamide, sulfanilamide and 2,4-diamino-6-phenyl-1,3,5-triazine, more preferably sulfanilamide is used.
Another preferred embodiment of co-crosslinkers (VII) useful in the present invention are described in U.S. patent application Ser. No. 09/008983, entitled xe2x80x9cLatent Catalysts for Epoxy Curing Systemsxe2x80x9d filed Jan. 20, 1998, by Gan et al.; which is incorporated herein by reference; and include for example copolymers of styrene and maleic anhydride having a molecular weight (Mw) in the range of from 1500 to 50,000 and an anhydride content of more than 15 percent. Commercial examples of these materials include SMA 1000, SMA 2000, and SMA 3000 having styrene-maleic anhydride ratios of 1:1, 2:1, and 3:1 respectively and having molecular weights ranging from 6,000 to 15,000; and which are available from Elf Atochem S.A.
When a co-crosslinker is used in the present invention, the co-crosslinker is present in an amount to crosslink less than 40% of stoichiometric amount needed to cure the epoxy resin. Preferably, the amount of the crosslinking agent in the epoxy resin is from 0 to 40% of the stoichiometric quantity needed to cure the epoxy content of the epoxy resin in the formulation.
The non-halogenated epoxy resin material (I) used in the present invention generally contains a phosphorus element or introduces a phosphorus element into the resin composition of the present invention. Generally, the epoxy resin material (I) is used in an amount of from about 30 wt% to about 95 wt%. The non-halogenated epoxy resin material component (I) may be selected from:(A) a non-halogenated phosphorus element-containing epoxy resin; or (B) a mixture of:(a) non-halogenated, non-phosphorus element-containing epoxy resin, and (b) a phosphorus element-containing compound which can be either reactive with or non-reactive with the non-halogenated non-phosphorous element-containing epoxy resin (C) the reaction product of: (c) a non-halogenated epoxy resin which can be either a phosphorous-element containing epoxy resin or a non-phosphorous-element containing epoxy resin; and (d) a phosphorus element-containing compound or (D) a combination of two or more of components (A) to (C).
Generally, the non-halogenated epoxy resin material (I) used in the present invention is a material which possesses on average more than 1 and preferably at least 1.8, more preferably at least 2 epoxy groups per molecule. In the broadest aspect of the present invention, the epoxy resin material may be any saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compound which possesses more than one 1,2-epoxy group.
In one preferred embodiment, the non-halogenated epoxy resin material (I) is a non-halogenated phosphorus element-containing epoxy resin (A) selected from those described in U.S. Pat. No. 5,376,453, incorporated herein by reference, including for example methyl diglycidyl phosphonate, ethyl diglycidyl phosphonate, propyl diglycidyl phosphonate, butyl diglycidyl phosphonate, vinyl diglycidyl phosphponate, phenyl digycidyl phosphonate and biphenyl diglycidyl phosphonate; methyl diglycidyl phosphate, ethyl diglycidyl phosphate, n-propyl diglycidyl phosphate, n-butyl diglycidyl phosphate, isohbutyl diglycidyl phosphate, allyl diglycidyl phosphate, phenyl diglycidyl phosphate, p-methoxyphenyl diglycidyl phosphate, p-ethoxyphenyl diglycidyl phosphate, p-propyloxyphenyl diglycidyl phosphate, p-isopropyloxyphenyl digycidyl phosphate, phenylthiodiglycidyl phosphate, triglycidyl phosphate, tris(glycidylethyl)phosphate, p-glycidyl-phenyl ethyl glycidyl phosphate, benzyl diglycidyl thiophosphate, and combinations thereof.
The non-halogenated phosphorus element-containing epoxy resin (A) can also be obtained by either:
(a) reacting an epoxy resin with a phosphorus element-containing compound capable of reacting with an epoxy resin; or
(b) epoxidizing a phosphorus element-containing compound, such as a diol.
Examples of a non-halogenated phosphorus element-containing epoxy resin (A) useful in the present invention which is obtained by reacting an epoxy resin with a phosphorus element-containing compound capable of reacting with an epoxy resin include:
(a) The reaction product of: (i) an epoxy novolac, such as D.E.N.* 438 or D.E.N.* 439 which are trademarks of and commercially available from The Dow Chemical Company; a trisepoxy such as Tactix 742 (Trademark of Ciba Geigy); a dicyclopentadiene phenol epoxy novolac; or a glycidyl of tetraphenolethane and (ii) a phosphorus element-containing compound reactive with the epoxy resin such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, such as xe2x80x9cSanko-HCAxe2x80x9d which is commercially available from Sanko of Japan, or xe2x80x9cStruktol Polydis PD 3710xe2x80x9d which is commercially available from Schill-Seilacher of Germany; or
(b) the reaction product of: (i) an epoxy novolac, such as D.E.N.* 438 or D.E.N.* 439; a trisepoxy such as Tactix 742; a dicyclopentadiene phenol epoxy novolac; a glycidyl of tetraphenolethane; a diglycidyl ether of bisphenol-A; or a diglycidyl ether of bisphenol-F and (ii) a phosphorus element-containing compound selected from 10-(2xe2x80x2,5xe2x80x2-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, such as xe2x80x9cSanko HCAxe2x80x94HQxe2x80x9d which is commercially available from Sanko of Japan; bis(4-hydroxyphenyl)phosphine oxide; tris(2-hydroxyphenyl_phosphine oxide; dimethyl-1-bis(4-hydroxyphenyl)-1-phenylmethylphonate; or tris(2-hydroxy-4/5-methylphenyl)phosphine oxide; or
(c) the reaction product of an epoxy resin and a phosphite; or
(d) the reaction product of an epoxy resin and a phosphinic acid.
Examples of a non-halogenated phosphorus element-containing epoxy resin (A) useful in the present invention which is obtained by epoxidizing a phosphorus element-containing compound include: the epoxidized product of a phosphorus element-containing compound such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide such as xe2x80x9cSanko-HCAxe2x80x9d commercially available from Sanko of Japan or xe2x80x9cStruktol Polydis PD 3710xe2x80x9d commercially available from Schill-Seilacher of Germany; 10-(2xe2x80x2,5xe2x80x2-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (such as xe2x80x9cSanko HCAxe2x80x94HQxe2x80x9d); bis(4-hydroxyphenyl)phosphine oxide; tris(2-hydroxyphenyl)phosphine oxide; dimethyl-1-bis(4-hydroxyphenyl)-1-phenylmethylphonate; tris(2-hydroxy-4/5-methylphenyl)phosphine oxide tris(4-hydroxyphenyl)phosphine oxide, bis(2-hydroxyphenyl)phenylphosphine oxide, bis(2-hydroxyphenyl)phenylphosphinate, tris(2-hydroxy-5-methylphenyl)phosphine oxide; or mixtures thereof. The epoxidizing of the phosphorus element-containing compound is usually carried out with an epihalohydrin such as epichlorohydrin well known to those skilled in the art.
In still another example of the epoxy resin (A) useful in the present invention is an epoxy resin which is the reaction product of an epoxy compound containing at least two epoxy groups and a chain extender as described in WO 99/00451, incorporated herein by reference. The preferred reaction product described in WO 99/00451 useful in the present invention is an epoxy-polyisocyanate adduct or an epoxy-terminated polyoxazolidone as described in U.S. Pat. No. 5,112,931, incorporated herein by reference. The isocyanate compounds as chain extenders include for example MDI, TDI and isomers thereof.
In another preferred embodiment, the non-halogenated epoxy resin material (I) used in the present invention is (B) a blend or a mixture of (a) non-halogenated, non-phosphorus element-containing epoxy resin compound containing at least two epoxy groups, and (b) a phosphorus element-containing compound. In other words, it is possible to add the phosphorus element-containing compound and the epoxy resin compound mixture to the overall resin composition of the present invention in order to form a non-halogenated phosphorus element-containing epoxy resin material (I) in-situ.
The phosphorus element-containing compound or monomer useful in the present invention contains some reactive groups such as a phenolic group, an acid group, an amino group, an acid anhydride group, a phosphite group, or a phosphinate group which can react with the epoxy groups of the non-halogenated, non-phosphorus element-containing epoxy resin compound.
The phosphorus element-containing compound of the present invention may contain on average one or more than one functionality capable of reacting with the epoxy groups. Such phosphorus element-containing compound preferably contains on average 0.8 to 5, more preferably 0.9 to 4, and most preferably 1 to 3 functional groups capable of reacting with epoxy resin.
The phosphorus element-containing compounds useful in the present invention include for example one or more of the following compounds: Pxe2x80x94H functional compounds such as for example HCA, dimethylphosphite, diphenylphosphite, ethylphosphonic acid, diethylphosphinic acid, methyl ethyiphosphinic acid, phenyl phosphonic acid, phenyl phosphinic acid, vinyl phosphoric acid, phenolic (HCAxe2x80x94HQ) and the like; tris(4-hydroxyphenyl)phosphine oxide, bis(2-hydroxyphenyl)phenylphosphine oxide, bis(2-hydroxyphenyl)phenylphosphinate, tris(2-hydroxy-5-methylphenyl)phosphine oxide; acid anhydride compounds such as M-acid-AH and the like; and amino functional compounds such for example bis(4-aminophenyl)phenylphosphate, and mixtures thereof. The chemical structure of some of the compounds described above are as follows: 
wherein X is CR3R4xe2x80x94(CR1R2)nxe2x80x94CR5R6 or o-phenylidene, n is 0 or 1 and R1-R8 may be the same or different and represent H, CH3, or C2H5. 
The phosphorus element-containing compounds useful in the present invention may also include those compounds having epoxy groups such as those compounds described above as compound (A) for example those having the following structures: 
wherein R is independently a hydrogen or an alkyl group from C1-C10 such as methyl, ethyl, etc.
In a most preferred embodiment of the present invention, the phosphorus element-containing monomer used in the present invention is for example, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide such as xe2x80x9cSanko-HCAxe2x80x9d commercially available from SANKO of Japan or xe2x80x9cStruktol Polydis PD 3710xe2x80x9d commercially available from Schill-Seilacher of Germany; 10-(2xe2x80x2,5xe2x80x2-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (such as xe2x80x9cSanko HCAxe2x80x94HQxe2x80x9d); bis(4-hydroxyphenyl)phosphine oxide; tris(2-hydroxyphenyl)phosphine oxide; dimethyl-1-bis(4-hydroxyphenyl)-1-phenylmethylphonate; tris(2-hydroxy-4/5-methylphenyl)phosphine oxide; tris(4-hydroxyphenyl)phosphine oxide, bis(2-hydroxyphenyl)phenylphosphine oxide, bis(2-hydroxyphenyl)phenylophosphinate, tris(2-hydroxy-5-methylphenyl)phosphine oxide; or mixtures thereof.
Other phosphorus element-containing compounds which can be used in the present invention, such as isomer mixtures of tris(2-hydroxyhpenyl)phosphine oxides, are described in co-pending U.S. Patent Application entitled xe2x80x9cPhosphorus Element-Containing Crosslinking Agents and Flame Retardant Phosphorus Element-Containing Epoxy Resin Compositions Prepared Therewithxe2x80x9d Attorney Docket No. 42190, filed of even date herewith, incorporated herein by reference.
The non-halogenated, non-phosphorus element-containing epoxy resin compound useful in the present invention is preferably a compound which has no alkyl aliphatic substituents or has a low amount of alkyl aliphatic sub stituents, such as for example the glycidyl ether of a phenol novolac, or the glycidyl ether of bisphenol-F, the glycidyl ether of bisphenol-S, bisphenol-A, or dihydroxyl ether of fluorene 9-bisphenyl; or trisepoxy, or dicyclopentadiene modified phenol epoxy resin, or mixtures thereof.
The most preferred epoxy resins are epoxy novolac resins (sometimes referred to as epoxidized novolac resins, a term which is intended to embrace both epoxy phenol novolac resins and epoxy cresol novolac resins). Such epoxy novolac resin compounds have the following general chemical structural formula: 
wherein xe2x80x9cRxe2x80x9d is hydrogen or a C1-C3 alkyl, e.g., methyl; and xe2x80x9cnxe2x80x9d is 0 or an integer from 1 to 10. xe2x80x9cnxe2x80x9d preferably has an average value of from 0 to 5. The preferred epoxy novolac resin is when R is preferably a hydrogen in the above Formula II.
Epoxy novolac resins (including epoxy cresol novolac resins) are readily commercially available, for example under the trade names D.E.N.(trademark) (Trademark of The Dow Chemical Company), and Quatrex(trademark) and tris epoxy such as Tactix(trademark) 742 (Trademarks of Ciba). The materials of commerce generally comprise mixtures of various species of the above formula and a convenient way of characterizing such mixtures is by reference to the average, nxe2x80x2, of the values of n for the various species. Preferred epoxy novolac resins for use in accordance with the present invention are those in which nxe2x80x2 has a value of from about 2.05 to about 10, more preferably from about 2.5 to about 5.
In yet another embodiment, the non-halogenated epoxy resin material (I) added to the overall resin composition of the present invention may be (C) the reaction product of: (c) a non-halogenated epoxy resin and (d) a phosphorus element-containing compound capable of reacting with the non-halogenated epoxy resin. The non-halogenated epoxy resin may be the same as the non-halogenated phosnhorous element-containing epoxy resin or the non-halogenated non-phosphorous element-containing epoxy resin as described above. The phosphorus element-containing compound may be the same as the phosphorus compounds as described above. Examples of the phosphorus element-containing compounds useful in the present invention also include the phosphorus compounds described in EP 0806429, incorporated herein by reference.
The compositions of the present invention may contain a catalyst (III) capable of promoting the reaction between the multi-functional phenolic cross-linker and/or the phosphorus element-containing compound with the epoxy resin and promoting the curing of the epoxy resin.
Examples of suitable catalyst materials (III) useful in the present invention include for example compounds containing amine, phosphine, ammonium, phosphonium, arsonium or sulfonium moieties. Particularly preferred catalysts are heterocyclic nitrogen-containing compounds.
The catalysts (as distinguished from cross-linkers) preferably contain on average no more than about 1 active hydrogen moiety per molecule. Active hydrogen moieties include hydrogen atoms bonded to an amine group, a phenolic hydroxyl group, or a carboxylic acid group. For instance, the amine and phosphine moieties in catalysts are preferably tertiary amine or phosphine moieties; and the ammonium and phosphonium moieties are preferably quaternary ammonium and phosphonium moieties.
Among preferred tertiary amines that may be used as catalysts are those mono- or polyamines having an open-chain or cyclic structure which have all of the amine hydrogen replaced by suitable substituents, such as hydrocarbyl radicals, and preferably aliphatic, cycloaliphatic or aromatic radicals.
Examples of these amines include, among others, 1,8-diazabicyclo(5.4.0) undec-7-en (DBU), methyl diethanol amine, triethylamine, tributylamine, dimethyl benzylamine, triphenylamine, tricyclohexyl amine, pyridine and quinoline. Preferred amines are the trialkyl, tricycloalkyl and triaryl amines, such as triethylamine, triphenylamine, tri-(2,3-dimethylcyclohexyl)amine, and the alkyl dialkanol amines, such as methyl diethanol amines and the trialkanolamines such as triethanolamine. Weak tertiary amines, for example, amines that in aqueous solutions give a pH less than 10 in aqueous solutions of 1 M concentration, are particularly preferred. Especially preferred tertiary amine catalysts are benzyldimethylamine and tris-(dimethylaminomethyl) phenol.
Examples of suitable heterocyclic nitrogen-containing catalysts include those described in U.S. Pat. No. 4,925,901. Preferable heterocyclic secondary and tertiary amines or nitrogen-containing catalysts which can be employed herein include, for example, imidazoles, benzimidazoles, imidazolidines, imidazolines, oxazoles, pyrroles, thiazoles, pyridines, pyrazines, morpholines, pyridazines, pyrimidines, pyrrolidines, pyrazoles, quinoxalines, quinazolines, phthalozines, quinolines, purines, indazoles, indoles, indolazines, phenazines, phenarsazines, phenothiazines, pyrrolines, indolines, piperidines, piperazines and combinations thereof. Especially preferred are the alkyl-substituted imidazoles; 2,5-chloro-4-ethyl imidazole; and phenyl-substituted imidazoles, and mixtures thereof. Even more preferred are N-methylimidazole; 2-methylimidazole; 2-ethyl-4-methylimidazole; 1,2-dimethylimidazole; and 2-methylimidazole. Especially preferred is 2-phenylimidazole.
Preferably, a Lewis acid (IV) is also employed in the composition of the present invention, especially when the catalyst (III) is particularly a heterocyclic nitrogen-containing compound.
Examples of heterocyclic nitrogen-containing catalysts(III), which are preferably used in combination with Lewis acids (IV) are those described in EP A 526488, EP A 0458502, and GB A 9421405.3, incorporated herein by reference. The Lewis acids useful in the present invention include for example halides, oxides, hydroxides and alkoxides of zinc, tin, titanium, cobalt, manganese, iron, silicon, aluminum, and boron, for example Lewis acids of boron, and anhydrides of Lewis acids of boron, for example boric acid, metaboric acid, optionally substituted boroxines (such as trimethoxyboroxine), optionally substituted oxides of boron, alkyl borates, boron halides, zinc halides (such as zinc chloride) and other Lewis acids that tend to have a relatively weak conjugate base. Preferably the Lewis acid is a Lewis acid of boron, or an anhydride of a Lewis acid of boron, for example boric acid, metaboric acid, an optionally substituted boroxine (such as trimethoxy boroxine, trimethyl boroxine or triethyl boroxine), an optionally substituted oxide of boron, or an alkyl borate. The most preferred Lewis acid is boric acid. These Lewis acids are very effective in curing epoxy resins when combined with the heterocyclic nitrogen-containing compounds, referred to above.
The Lewis acids and amines can be combined before mixing into the formulation or by mixing with the catalyst in-situ, to make a curing catalyst combination. The amount of the Lewis acid employed is preferably at least 0.1 moles of Lewis acid per mole of heterocyclic nitrogen compound, more preferably at least 0.3 moles of Lewis acid per mole of heterocyclic nitrogen-containing compound.
The formulation preferably contains no more than 5 moles of Lewis acid per mole of catalyst, more preferably contains no more than 4 moles of Lewis acid per mole of catalyst and most preferably contains no more than 3 moles of Lewis acid per mole of catalyst. The total amount of the catalyst is from about 0.1 wt % to about 3 wt %, based on the total weight of the composition, preferably from about 0.1 wt % to about 2% wt %.
The compositions of the present invention may also optionally contain one or more additional flame retardant additives (V), including for example, red phosphorus, encapsulated red phosphorus or liquid or solid phosphorus-containing compounds, for example, ammonium polyphosphate such as xe2x80x9cExolit 700xe2x80x9d from Clariant GmbH, a phosphite, or phosphazenes; nitrogen-containing fire retardants and/or synergists, for example melamines, melem, cyanuric acid, isocyanuric acid and derivatives of those nitrogen-containing compounds; halogenated flame retardants and halogenated epoxy resins (especially brominated epoxy resins); synergistic phosphorus-halogen containing chemicals or compounds containing salts of organic acids; inorganic metal hydrates such as Sb2O3, Sb3O5, aluminum trihydroxide and magnesium hydroxide such as xe2x80x9cZerogen 30xe2x80x9d from Martinswerke GmbH of Germany, and more preferably, an aluminum trihydroxide such as xe2x80x9cMartinal TS-610xe2x80x9d from Martinswerke GmbH of Germany; boron-containing compounds; antimony-containing compounds; and combinations thereof. Examples of suitable additional flame retardant additives are given in a paper presented at xe2x80x9cFlame retardantsxe2x80x94101 Basic Dynamicsxe2x80x94Past efforts create future opportunitiesxe2x80x9d, Fire Retardants Chemicals Association, Baltimore Marriot inner harbour hotel, Baltimore Md., Mar. 24-27, 1996.
When additional flame retardants which contain a halogen is used in the composition of the present invention, the halogen-containing flame retardants are present in amounts such that the total halogen content in the epoxy resin composition is less than 10 wt %.
When additional flame retardants which contain phosphorus are present in the composition of the present invention, the phosphorus-containing flame retardants are generally present in amounts such that the total phosphorus content of the epoxy resin composition is from about 0.2 wt % to about 5 wt %.
Also, optionally, other non-flame retardant additives such as inorganic fillers (VI) may be used in the composition of the present invention and may include, for example, talc.
When an inorganic flame retardant, a non-flame retardant or a filler is used in the present invention, the amount of additive or filler present in the epoxy resin composition of the present invention is generally form 0 wt % to about 40 wt %; preferably less than 30 wt % and more preferably less than 10 wt %, depending on the end use application of the epoxy resin composition.
The epoxy resin composition of the present invention may also optionally contain other additives of a generally conventional type including for example, stabilizers, other organic or inorganic additives, pigments, wetting agents, flow modifiers, UV light blockers, and fluorescent additives. These additives can be present in amounts of from 0 to about 5 weight percent, preferably from less than about 3 weight percent. Examples of suitable additives are also described in U.S. Pat. No. 5,066,735 and in C.A. Epoxy Resinsxe2x80x94Second Ed. at pages 506-512 (Mercel Dekker, Inc. 1988).
Solvents (VIII) may also optionally be used in the composition of the present invention. When a solvent is used it may include for example, propylene glycolmethylether (Dowanol PM(trademark)), methoxypropylacetate (Dowanol PMA(trademark)), methylethylketone (MEK), acetone, methanol, and combinations thereof. When a solvent is used in the present invention, the amount of solvent present in the epoxy resin composition of the present invention is generally form 0 wt % to about 50 wt %; preferably from about 10 wt % to about 40 wt % and more preferably from about 10 wt % to about 35 wt %, depending on the end use application of the epoxy resin composition.
Optionally, in some applications it may be desirable to add a small amount of a halogenated epoxy resin (IX), provided the halogenated epoxy resin is added in an amount such that the halogen content of the overall epoxy resin composition of the present invention is less than 10 weight percent.
The compositions of the present invention can be produced by mixing all the components together in any order. Preferably, compositions of the present invention can be produced by preparing a first composition comprising the epoxy resin, and the second composition comprising the multi-functional phenolic hardener. Either the first or the second composition may also comprise a phosphorus element-containing compound, a curing catalyst and/or a nitrogen-containing co-cross-linking agent. All other components may be present in the same composition, or some may be present in the first, and some in the second The first composition is then mixed with the second composition, and cured to produce a fire retardant epoxy resin.
The compositions of the present invention can be used to make composite materials by techniques well known in the industry such as by pultrusion, moulding, encapsulation, or coating.
The present invention is particularly useful for making B-staged prepregs and laminates by well known techniques in the industry.
A number of preferred embodiments of the present invention are illustrated, in the following specific Examples.